Secondhand Pot Smoke Just As Bad For Heart As Tobacco Interview with:

Matthew L. Springer, Ph.D. Professor of Medicine Division of Cardiology University of California, San Francisco San Francisco, CA

Dr. Matthew Springer

Matthew L. Springer, Ph.D.
Professor of Medicine
Division of Cardiology
University of California, San Francisco
San Francisco, CA What is the background for this study?

Response: We’ve known for many years that secondhand smoke from tobacco cigarettes is harmful, and the vast majority of deaths thought to result from secondhand smoke are from cardiovascular disease. However, very little has been known about cardiovascular consequences of exposure to secondhand smoke from marijuana, and people tend to mistake the lack of evidence that it is harmful, for evidence that is it not harmful. As a result, many people seem relatively unconcerned about smoking marijuana and being exposed (or exposing others) to marijuana secondhand smoke. Politicians and policy makers also seem less willing to limit where people can smoke marijuana (under legal circumstances) than tobacco. What has been lacking is research into how exposure to marijuana smoke affects cardiovascular health. It has been difficult to do such experiments because marijuana is illegal in the eyes of the federal government. However, we have been studying the harmful effects of secondhand tobacco smoke on the function of rat blood vessels, which is similar to its harmful effects on human blood vessels, and we now have studied how the function of rat blood vessels is affected by exposure to secondhand marijuana smoke. What are the main findings?

Response: The main finding was that when rats were exposed to secondhand smoke from marijuana for one minute, their arteries became less efficient at carrying enough blood for at least 90 minutes, whereas similar exposure to secondhand smoke from tobacco caused impairment that fully recovered within 30 minutes (exposure to clean air in the exposure chamber did not cause impairment). (It is important to understand that arteries of rats and humans are similar in how they respond to tobacco smoke, so the response of rat arteries to marijuana smoke is expected to be a valid indication of how human arteries respond to marijuana smoke.) This impairment of function occurred even when the marijuana was burned without rolling paper and when we used marijuana from which all of the cannabinoids had been removed; it is a result of inhaling burning plant smoke. What should readers take away from your report?

Response: The main message for the public is that inhalation of smoke should be avoided, regardless of whether it comes from tobacco, marijuana, or other sources. Inhaling smoke is bad for you, period. We instinctively avoid inhaling smoke under most circumstances (such as around a campfire), and people would be better off if they can apply that instinct to any kind of smoke.

For healthcare providers, I see two messages. First, if prescribing medical marijuana, it’s advisable to caution the patient that smoking it may cause similar cardiovascular problems as smoking tobacco, and that they should avoid exposing others (their families, friends, bystanders in public) to their smoke just like they would avoid exposing others to their tobacco smoke if they used cigarettes. There are ways to take medical marijuana that don’t involve smoke generation.

Second for the doctors, if they are asking their patients general healthy lifestyle questions that include “are you smoking” and “are you being exposed to secondhand smoke,” it would be helpful to clarify to the patient that this refers to smoke from tobacco AND marijuana.

There is also a message for politicians and policy makers, which is that laws and regulations that protect the public from unwanted exposure to smoke should be written to specifically include marijuana as well as tobacco. Even if the marijuana is being smoked for medical reasons, other people nearby or in the same room are being exposed to smoke that could be even worse for them than tobacco smoke. What recommendations do you have for future research as a result of this study?

Response: Ever since we reported our initial findings, I have heard directly or indirectly from many people who consider switching from smoking marijuana to using leaf vaporizers, which would potentially avoid the combustion smoke chemicals that cause the problems we’ve observed. These gently heat the buds and leaves and cause the THC (and potentially some other chemicals) to evaporate off of the surface of the plant material, without causing combustion or smoke. This may be a valid healthy change, but we do not know this for sure, and we will soon be studying the leaf vaporizers to see if exposure of the rats to these devices will or will not cause these cardiovascular problems. It will also be important to learn more about what the real-world levels are of marijuana smoke in various social situations, so that researchers can more accurately model experiments to what people actually experience. Is there anything else you would like to add?

Response: What I would really like to happen next is that in the debates that have been taking place in governments around the country and beyond, about whether the public should be protected from unintentional marijuana smoke exposure as it is protected from tobacco smoke exposure, we stop hearing people say that “there is no scientific evidence that secondhand marijuana smoke is harmful” and instead hear “secondhand marijuana smoke may be harmful.” Thank you for your contribution to the community.


One Minute of Marijuana Secondhand Smoke Exposure Substantially Impairs Vascular Endothelial Function
Xiaoyin Wang, MD; Ronak Derakhshandeh, MS; Jiangtao Liu, MD; Shilpa Narayan, BS;* Pooneh Nabavizadeh, MD; Stephenie Le, BA;† Olivia M. Danforth, BS;‡ Kranthi Pinnamaneni, MD; Hilda J. Rodriguez, AS; Emmy Luu, BS; Richard E. Sievers, BS; Suzaynn F. Schick, PhD; Stanton A. Glantz, PhD; Matthew L. Springer, PhD
Journal of the American Heart Association
DOI: 10.1161/JAHA.116.003858

Note: Content is Not intended as medical advice. Please consult your health care provider regarding your specific medical condition and questions.

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Last Updated on July 27, 2016 by Marie Benz MD FAAD